In the construction of foundations, an extended length continuous concrete pile may be formed by joining two or more pile units end to end. The requirement for piles of extended length is increasing. As structures are built taller and with greater concentration of weight, the foundation to remain stable through the life of the building must be deeper, often deep enough to rest on bedrock below several hundred feet of overburden. Foundations having 400 feet deep or more pile bases are not now uncommon.
When concrete piles are joined end to end, the joint must have a cross section no larger in any dimension than the non-jointed section of the piling. The joints must also be as strong as the non-jointed piling in order to remain straight so that the jointed pile will drive vertically true during the high stress pile driving process.
A variety of concrete pile joining devices have been disclosed in the past; all of these earlier devices have exhibited one or more serious limitations when put into practical usage. Most of these earlier devices required a male and a female element along with various fasteners to form a joint. The need for two kinds of joining elements increases the inventory requirements, and is an added complication in field assembly of jointed piles. While some of these earlier joining devices utilized two identical members to complete the joint, all of the earlier joining devices of diverse or identical elements lacked resistance to bending or torsion loads even though all appeared to have good compression load resistance. None of these earlier devices exhibited strength in all modes of loading and also exhibited convenience of assembly in the field.
When a concrete pile of extended length formed by axially coupling a number of sections is driven into place, even minute differences in axial alignment in the joints will result in large deflection of the pile at its leading end. In other words, for long jointed piles, the coupling joints must align the joined piles with precision. The earlier disclosed pile joints all permit considerable tolerance in the joint alignment. For piles having only two or three joined sections, these conventional alignment tolerances are not critical. However, in a jointed pile of six or 10 joined sections, a closely held precision of alignment is critical to constructing a dependable foundation structure.
Another serious limitation on all the earlier disclosed pile joint device resides in the manner in which, in these respective earlier devices, the joint element is mounted to and receives the load forces from the concrete portion of the pile and from the metal reinforcing structures imbedded within the concrete. In these earlier devices, the end joint elements attached respectively to the extreme ends of the concrete piles often resulted in excessively high stresses within the concrete sections adjacent to the joining element. While the joint in these earlier devices may survive application of large loads, the concrete pile often fractured in the high stress zone. Notwithstanding, the long practice in foundation construction of joining pile sections to form an extended length pile, there remains a need for a high strength, precision aligned, easily assembled, low cost simple pile coupling device.